Neonympha mitchellii is an endangered species of nymphalid butterfly of the eastern United States. There are two known subspecies:

• N. m. mitchellii, the nominate subspecies, commonly called Mitchell's satyr or Mitchell's marsh satyr, is found in Michigan and Indiana. The species is presumably extirpated from former ranges in Ohio (last seen in the 1950s), New Jersey (last seen in 1988), and Wisconsin.
• N. m. francisci, commonly called Saint Francis' satyr, is found in a single metapopulation in a 10 × 10 km area of Fort Bragg in North Carolina.

Recent discoveries since 1998 of populations in Alabama, Mississippi, and Virginia are being studied for taxonomic classification, and may be grouped with N. m. mitchellii or be described as new subspecies.

All subspecies, including those newly discovered, are federally protected under the Endangered Species Act.

Its larvae can feed upon the highly-invasive Japanese stilt grass Microstegium vimineum, so populations of this butterfly are potentially at risk from efforts to remove stilt grass. A butterfly of similar appearance, the Carolina satyr (Hermeuptychia sosybius), is also able to feed upon stilt grass.

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